Saline coatings and process of making the same



Patented Nov. 22, 1932 UNITED STATES .PATENT OFFICE FERDINAND na "l arn, on uccnn, BELGIUM, assranoa 'ro LA soummn mnc'ramun AuroeENE s. a, on naussnnannnsmu SALINE COATINGS AND EBOCESS OF MAKING THE SAME No Drawing. Application filed November 12, 1928,

This invention relates to a process of mak-' .ing saline compositions suitable for use as a welding flux and intended to form the flux coatings of welding rods and of electrodes used for welding non-ferrous metals by the electric are.

In the metallurgy of metals other than iron and in particular in the metallurgy and the welding operations carried out by means of the gas blow pipe, of the light metals such as aluminium, it is known to use essentially .water soluble saline compounds as a flux,

reasons (for instance, the destructive action of salts on organic binders, the difference in the solubility coefiicients of the salts, respectively, and the coagulating action of water soluble salts in general on known inorganic binders such as alkaline silicate solutions), it was not possible to supply suitable saline mixtures in a colloidal, plastic or viscous form enabling a paste or coating to be ob tained which was capable of being applied to, and of drying on, the arts to be welded (in the case of butt wel g) or bn weld sticks and electrodes used in arc welding.

The present invention provides a new practical method of making saline welding composition comprising watersoluble compounds, and capable of belng a plied as a paste to form by desiccation, a ry and adherent coating for instance by application on weldin rods or soldering sticks or metallic electro es used in arc welding.

The invention comprises a process in which thesilica of a solution of an alkali metal silicate is dis ersed with water soluble com- (pounds which enter into the flux forming composition and which at the same time com: bine chemically with the alkali of said alkali metal silicate solution.

In other words and in a broader form of.

execution of the invention, water soluble compounds (salts) which enter into the flux forming coating, are added to and ground Serial No. 319,023, and'in France June 2a, 1928.

with a solution of an alkali metal silicate, and in the resulting mixture in which the sllicate is separated from the alkali of said solution, a water soluble compound is added, which chemically combines the alkali and at the same time disperses physically said gelatinous silica.

From the collodial chemistry point of view, the degree of dispersion of the gel of silidais what is called the true dispersion and cannot be confounded with the degree of dispersion of a.colloidal solution or sol. This particular step of the rocess, which leads to said true dispersion o the gelatinous silica and which at the same time neutralizes the freed alkali, in the presence of water soluble sa lts, will hereinafter be called the acidpeptization or for short peptization step.

From a physical point of view, the compositions according to the invention are essentially composed of a mixture of water soluble salts, partly in suspension and partly in solution, the said salts forming with dispersed silica a particular colloidal system that is to say a viscous and fluid paste .0 saline particles which is capable of drying and agglutinating .on a metallic support, to which they then solidly adhere.

Other details of the process according to the invention are to be found in the examples given below.

L Example 1 a A paste for coating aluminium welding rods is prepared as follows: 4

A mixture of alkaline chlorides which enter into the composition of said coating and which comprises 7 O to parts in weight 0 of about 4.0)

dispersion or peptization agent HF) which combines -the alkali can be replaced by an equivalent acid salt for example potassiumhydrogen fluoride (KEHF) which is a more handy form of fluorhydric acid, and which canadvantageously increase, if desired, the

percentage of fluoride in the composition.

The combination of the alkali with the agent of dispersion, with the formation of a salt in situ cannot be considered as a direct neutralization as considered in elementary chemistry because adsorption phenomena inherent to the particular colloidal system obtained in this process are able to keep an acid and a base present without their reacting immediately upon each other to effect mutual neutralization.

To obtain a final product, substantially neutral, or even slightly acid, the acidpeptization step can nevertheless be controlled, by controlling the'pH value of the paste by a known method.

Example 93' The coating thus prepare may be rendered more fluid by addition of water. Furthermore, it vhas been found that when the peptization has been suitably effected, the colloidal system is sufiiciently stable to allow of incor or'ating therein one or more other crystaL' loi s gater soluble salts) in aqueoussolution.

oreover, after peptization, it is possible, according to the invention, to incorporate in the colloidal system formed, one or more crystalloidal salts, soluble or slightl soluble inwater, in the solid state, by grin ing. According to this particular feature of the invention, i-t is possible, for example, to

incorporate in the coating, easily-decomposn able salts, without decomposing them and whose properties it is desired to preserve in the drled paste of coating.

Example 3 ture obtained according to Example 2. After the salts have been absorbed in the colloidal system, and for the purpose already deiout the invention are possible. Thus, for

example, in producing a. coating composition according to the specific Example 1, the fluorhydric acid disperses the silica and combines the alkali, forming a fluoride, while in the Example 2 the dispersion of the silica and combination of the alkali is effected by phosphoric acid.

In this second example, however, according to the proportions of the compounds used, the added phosphoric acid may eventually decompose a fraction of the fluoride of potassium, forming a phosphate and liberating a corresponding quantity of fluorhydric .acid whichin this case cooperates also in the acid peptization process.

Thus, in'a form of carrying out the process according to the Example 2, the decomposition step can for instance be started with a phosphate and/or phosphoric acid, the acid peptization being effected with a flouride or di-fluoride.

It is also" possible to add to the achieved. composition or' in the course of PIOdUCtIOH thereof, known adjuvants, for example, oxides, alkaline-earth or insoluble metallic carbonates, combustible substances such as carbon, or metallic substances or the like which do not interfere chemically in the pe tization step, but are intended, for examp e, to increase the refractory properties of the coating, to determine its melting point or to cause different effects in the are or in the formation of the welding slag.

Welding electrodes or rods which have been coated with the paste compositions are preferably dried in air at temperatures of about 80100 C.

The flux coating obtained according to the invention, for instance, those prepared as in Examples 1 or 2, 'may also be used on the articles which are to be welded (e. g. by buttwelding) or solderedJ What I claim is: 7b 1. A method of making welding composit ons in theform of a paste containing water soluble compounds, to form a dry coating for welding rods and electrodes used for arc welding, comprising dispersing the silica of an alkali metal silicate solution with water soluble compounds which enter into the flux forming composition and which at the same time chemically combine the alkali of said alkali metal silicate solution.

2. A method, of making welding compositions in the form of a paste containing water soluble compounds to form a dry coating for welding rods and electrodes used for are 180 welding, comprising the step of grinding together an alkali metal silicate solution with water soluble salts which-enter in the flux coating, and the step of adding to the resulting mixture, in which the silica is separated from the alkali of said solution, a compound of acid character which chemically combines the free alkali of said silicate solution, forming in situ a salt entering also in the composition, and at the same time disperses the said silica.

3. In amethod of the character described in claim 2, the addition of salts in aqueous solution to the resulting composition.

41 In a method of the character'described in claim 2, the addition of water solu le salts in solid form to the resulting composition.

I '5. In a method of the character described in claim 2, the addition to' the resulting composition of refractory insoluble compounds which remain chemically inert in the formation of the composition and modify the properties of said comfiosition.

In testimony -w ereof I afiix my signature.

FERDINAND DE PAPE. 

